1. Field of the Invention
The present invention relates to an automatic document feeder for automatically feeding and discharging a document onto and from a platen glass of an analog or a digital copying machine or image reading device.
2. Description of Related Art
In the art of electrophotographic copying machine, recently, various types of automatic document feeder (hereinafter referred to as ADF) have been provided so that copying efficiency can be improved. U.S. Pat. No. 4,285,512 and Japanese Patent Publication No. 62-25484 disclose such document feeders. Such an ADF has a conveyer belt which is endlessly laid between a driving roller and a driven roller such that it faces to a platen glass, and a document is slid on the platen glass with rotation of the conveyer belt. Conventionally, some back-up rollers are disposed inside the ring of the conveyer belt so as to press the belt on the document, which secures the conveyance of the document. A single roll or alternatively some ring rollers are used as the back-up roller.
The roll type back-up rollers may apply an uneven pressure to the document if the platen glass is deformed or if the ADF is set incorrectly. This will cause a skew of the document. The ring type back-up rollers may press a small size document with only one array of rings in respect to the document conveying direction. This will cause poor conveyance and a skew of the document.
Another problem is an exchange of conveyer belts. The conveyer belt is whitish and accordingly is soiled easily. The soiled conveyer belt degrades a copy image. For this reason, the conveyer belt must be cleaned or exchanged every certain period. In exchanging the conveyer belt, conventionally, a cover of the ADF must be removed, and the conveying section, including the driving roller, the driven roller and the back-up rollers, must be detached from the body of the ADF. Thus, the exchange of conveyer belts has been troublesome.
The ADF is fitted on the body of the copying machine by hinges at the rear side of the body and pivots on the hinges so that an operator can set a document on the platen glass manually. In order for secure conveyance of the document, the conveyer belt must be in contact with the platen glass entirely with an even pressure. However, because of errors in production of the parts and in assembly of the machine, a problem occurs in setting the conveyer belt on the platen glass. For example, because the level difference between the surface on which the hinges are fixed and the surface of the platen glass varies from machine to machine or because the surface on which the hinges are fixed and the surface of the platen glass may not be exactly parallel to each other, the conveyer belt cannot be in contact with the platen glass entirely with an even pressure.
Conventionally, in order to solve the problem, when the machine is set up, spacers are provided between the surface of the machine body and the hinges so that the level of the hinges can be adjusted to the level of the surface of the platen glass. However, this adjustment must be carried out differently and properly for each machine, and this is troublesome. In order to save the adjustment, a structure which can automatically set the conveying section in a correct position where the conveyer belt is in contact with the platen glass entirely with an even pressure is contrived. More specifically, the conveying section of the ADF is held by plates extended from the movable sides of the hinges with a clearance such that the conveying section can move up and down within the clearance. However, if the structure is simply adopted, since a conveyer belt motor and other heavy parts are disposed in the rear side of the conveying section, the front side of the conveying section may be lifted up with a shock or a vibration generated at a time of opening and closing the body of the copying machine.
A further problem is that the conveyer belt puts a manually set document out of position. When the ADF is pulled up from the copying machine for manual setting of a document, the conveyer belt slacks. Then, when the ADF is pushed down toward the platen glass, the slack part of the conveyer belt first comes into contact with the document set on the platen glass. Thereafter, as the ADF is pivoting down, the slack part moves toward the pivot of the ADF (rear side of the copying machine). With the movement of the slack part, the document set on the platen glass is moved to be out of position.